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1 When the burner of a stovetop is very hot, it is a source of heat energy. 2  Anything placed onto the stovetop and warmed, whether a pot of tea or a skillet for frying eggs, also become sources of heat energy. 3  Automobile fuels such as gasoline are sources of heat energy, as is the hot engine of a racecar or a school bus.
Geothermal energy is called a renewable energy source because the water is replenished by rainfall, and the heat is continuously produced by the earth. 2. History of Geothermal Energy. Many ancient peoples, including the Romans, Chinese, and Native Americans, used hot mineral springs for bathing, cooking, and heating.